The most common cause of primary septal panniculitis is erythema nodosum. The clinical and microscopic features causing this disease are well known to the experienced dermatologist.
The most common etiologic agents in erythema nodosum include infections (e.g. group A beta hemolytic strep, deep fungal and viral), drugs (e.g. oral contraceptives and sulfonamides), inflammatory bowel disease, sarcoidosis, pregnancy and malignancy.Dr. Robinson-Bostom says that, "We have found new associations concerning the etiologies in erythema nodosum. These include hepatitis C and HIV infections, all trans retinoic acid, echinacea herbal therapy, celiac disease, as well as carcinoid syndrome."